questions about room fire simulation

Now I'm tring to study simulate methane-air diffuse fire in building using fluent6. I setted Fluent with single-phase uncompressible fluids, k-e model with standard coefficients, standard wall function for near wall treatment, adopted The Eddy-Dissipation Model\Arrhenius model to simulate combustion in fire, and used p-1 radiation model. The structure of room is rectangular. Mesh is done with Gambit using hex-map. During the simulation, I have some question:

1. When I set room vent radiation boundary condition, it is atmosphere, I wonder which kind of vent to define inlet-vent or outlet-vent? And when i switch on external Black body temperature Method, how to set Specified external TemperatureBlack Body Temperature and Internal Emissivity?

2.I can't use P1 radiation model well, so can you tell me where i can find some message about it?

3. For k-e 2 equations model, coefficient C3 is calculated according to tanh/v/u/. Can I define C3 to constant using UDF?

4.What is different between internal wall Heat Transfer Coefficient and external wall Heat Transfer Coefficient? In fluent help, it say the fluid-side heat transfer coefficient is computed based on the local flow-field conditions in section 6.13.4.

5. Is the temperature in Arrhenius in average? why the reaction rate is tend to zero, the reason is about stiffness?

6.When I set methane velocity-inlet, and switch on Turbulence Specification Method, how to set turbulence intensity and Hydraulic Diameter£¿ So at the end of this: can someone help me?